Relative isotope composition values, e.g., relative carbon isotope composition values (δ13C values) can be used in a variety of ways to verify the origins of materials in a composition. Other substances within the composition may also be used to verify the origin of the material. Such techniques are useful in, e.g., confirming that a given composition contains substances sequestered from a particular source, e.g., fossil fuels, and such compositions may have a premium value.